THE OSI MODEL

ISO is the organization.OSI is the model.

ISOInternational Standards Organization

OSIOpen Systems Interconnection

THE MODEL

ApplicationApplication

PresentationPresentation

SessionSession

TransportTransport

NetworkNetwork

DatalinkDatalink

PhysicalPhysical

7

6

54

3

2

1

Layered Architecture

Application7-6 Interface

Presentation6-5 Interface

Session5-4 Interface

Transport4-3 Interface

Network3-2 Interface

Datalink2-1 Interface

Physical

Application7-6 Interface

Presentation6-5 Interface

Session5-4 Interface

Transport4-3 Interface

Network3-2 Interface

Datalink2-1 Interface

Physical

Network

Datalink

Physical

Network

Datalink

Physical

3rd

2nd

1st

3rd

2nd

1st

3rd

2nd

1st

Peer-to-peer protocol (7 th layer)

Peer-to-peer protocol (6 th layer)

Peer-to-peer protocol (5 th layer)

Peer-to-peer protocol (4 th layer)

Physical communication

Device A Device BIntermediatenode

Intermediatenode

7

6

5

4

3

2

1

7

6

5

4

3

2

1

Peer-to-peer Processes

Interface between Layers

Organization of the Layers

Layer 1 , 2 and 3 physical, data link and network Are network support layer;

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Layer 5 , 6 and 7 session , presentation and application

The user support layer; interoperability among unrelated software system

Layer 4 transport layer เป็�นส่วนเชื่#�อมูตัอระหวาง layer ท%�อย� บนและลาง (hardware ,software)

An exchange using the OSI model

L7 dataL7 dataH6

L6 data H5L5 data H4

L4 data H3L3 data H2T2

010101010101101010000010000

7654321

7654321

Transmission medium

L7 dataL7 dataH6

L6 data H5L5 data H4

L4 data H3L3 data H2T2

010101010101101010000010000

Function of the layers

Physical layer

L2 data

10101000000010

From data link layer

Physical layer

Transmission medium

L2 data

10101000000010

To data link layer

Physical layer

ส่(�งท%�จะพ(จารณ์าในข้�*นตัอนการท+างานข้อง physical layer

• Line configuration

• Data transmission mode

• Topology

• Signal

• Encoding

• Interface

• Medium

Data Link layer

L3 data

From Network layer

DataLink layer

H2T2 Frame

10101000000010

To Physical layer

L3 data

To Network layer

DataLink layer

H2T2 Frame

10101000000010

From Physical layer

Specific responsibilities of the data link layer include the following;

Node to node delivery

Addressing

Access control

Flow control

Error handling

Synchronization

LLCLogical Link ControlMACMedia Access Control

Example Data link layer

DataT2 10 87

Trailer Sourceaddress

Destinationaddress

10 28 53 65 87

Network layer

L4 data

From transport layer

To data link layer

H3 Packet

L3 data

Networklayer

L4 data

To transport layer

From data link layer

H3 Packet

L3 data

Networklayer

Specific responsibilities of the network layer include the following;

Source-to-destination delivery

Logical addressing

Routing

Address transformation

Multiplexing

10

Example Network layer

87

DataT2 10 20A PR

45

71

95 77

DataT2 66 95A P

DataT2 99 33A PRing

R33

66

99

20F

T

N

Z

Bus

Bus

G

EA

P

Transport layer

L5 data

From session layer

To network layer

H4

L4 data

Transportlayer H4 H4

L4 data

L4 data

L5 data

To session layer

From network layer

H4

L4 data

TransportlayerH4 H4

L4 data

L4 data

Specific responsibilities of the transport layer include the following;

End-to-end massage delivery

Service-point (port) addressing

Segmentation and reassemble

Connection control

Example Transport layer

Data j k

A

Data2 j k A P

Data1 j k A P

Data2 j k A P H2T2

Data1 j k A P H2T2

Data j k

B

Data2 j k A P

Data1 j k A P

Data2 j k A P H2T2

Data1 j k A P H2T2

Physical linkPhysical link

Transport layer

Networklayer

Data linklayer

Session layer

L6 data

From presentation layer

To transport layer

L5 data

H5

Sessionlayer

syn syn syn

L6 data

To presentation layer

From transport layer

L5 data

H5

Sessionlayer

syn syn syn

Specific responsibilities of the session layer include the following;

Session management

Synchronization

Dialog control

Graceful close

Presentation layer

L7 data

From application layer

To session layer

L6 data

Presen-tationlayer

Encode,encrypted,andCompresses data

H6

L7 data

To application layer

From session layer

L6 data

Presen-tationlayer

Encode,encrypted,andCompresses data

H6

Specific responsibilities of the presentation layer include the following;

Translation

Encryption

Compression

Security

Application layer

To presentation layer

L7 data

Applicationlayer

X.500 FTAM X.400

User

From presentation layer

L7 data

Applicationlayer

X.500 FTAM X.400

User

Specific responsibilities of the application layer include the following;

Network virtual terminal

File access transfer,and management

Mail services

Directory services

Summary of Layer Function

Application

Presentation

Session

Transport

Network

Data Link

Physical

To allow access to network resources

To translate,encrypt, and compress data

To establish,manage,and terminate sessionTo provide reliable end to end message Delivery and error recoveryTo move packets from source to Destination; to provide internetworkingTo organize bit into frames; to provideNode to node deliveryTo transmit bits over a medium; toProvide mechanical and electrical specification